This invention relates to apparatus for the conversion of salt water to fresh water and to a method for performing such conversion.
Many suggestions have been made for the desalination of salt water, such as the use of solar stills, multiple effect distillations, flash distillations, freezing, vapor compression and others, but few of these proposals have proved to be practical, primarily because of the high energy cost in performing the process or the high cost for the equipment or the inefficiency of the proposed method or apparatus.
In the present invention, saline water is heated on an evaporation surface and the water vapor is moved by means of a fresh water stream. This system includes an evaporation tank and a fresh water tank. Fresh water and water vapor is pumped from the fresh water tank into a condensation chamber in the evaporation tank, increasing pressure and temperature to cause a film of salt water arranged thereabove on an evaporation surface to vaporize, and leaving salts and other impurities on the evaporation surface for flushing therefrom. The fresh water flow is returned to the fresh water tank.
The condensation chamber is arranged in the evaporation tank below the evaporation surface. The evaporation surface has maximum surface area in contact with the feed water delivered to it. The fresh water stream entrains vapor and routes this entrained fresh water--vapor stream into the condensing chamber, where, upon condensation, the heat of vaporization passes through the upper wall of the condensation chamber at or close to the evaporation surface, transfering its heat to vaporize the saline water passing onto the evaporation surface.
An outlet in the condensation chamber directs fresh water and distillate to the fresh water tank. The system also includes means for purging salt and other impurities left in the concentrated salt water at the evaporation surface during the vaporization process, as well as heat transfer means for conserving energy in the system. Preferably, the tanks, conduit and pumps are well insulated to prevent unintended loss of heat. Also, preferably, the system is relatively compact, as to permit the process to be performed with portable equipment, such as could be mounted on a flat bed trailer.
Once the system is brought to temperature and evaporization--vaporization begins, through the use of valves and conduits, and directing of the flow by means of one or more pumps, the process can be performed continuously, and fresh water may be taken off regularly. Depending upon the balancing of flow and the amount of water desired to be processed, the system may be tuned to accommodate the requirements for fresh water.